UV-curable adhesion promoter, laminated structures using same and methods for fabricating such laminated structures

ABSTRACT

An adhesion promoter for enhancing the bond between adjacent layers of a multilayer structure to prevent delamination thereof is disclosed. The adhesion promoter comprises an aromatic polyimide-based UV-cured acrylate. Also disclosed are laminated structures including liquid crystal displays and bonded missile domes that utilize an adhesion promoter of the invention, and methods for fabricating such structures.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/434,641, filed May 15, 2006, titled “UV Curable AlignmentMaterial for Fabrication of Monolithic Compensators for Liquid CrystalDisplays”, which in turn is a continuation-in-part of U.S. patentapplication Ser. No. 11/241,070, filed Sep. 30, 2005 and titled “New LowTemperature Low Cost Liquid Crystal Alignment Material”; both of theforegoing applications are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to laminated optical apparatus andparticularly to the prevention of the delamination of such apparatus.

BACKGROUND OF THE INVENTION

One example of a laminated optical apparatus is a thin film flat paneldisplay such as a liquid crystal display (LCD). LCDs exist in amultitude of embodiments depending upon the specific type of liquidcrystal material and the configuration of the polarizers and electrodes.In its simplest form, a typical LCD comprises a liquid crystal cellsituated between a pair of optically transparent substrates each ofwhich has an outer surface that may be coated with a polarizer layer.

Many LCDs exhibit optical performance that is highly sensitive to theangle at which the display is viewed. Optical compensation layers, alsoreferred to as compensators or retarders, are commonly used to mitigatethe viewing angle effects in LCDs. Such a compensator or retarder layermay be applied directly to the outer surface of each substrate so as tobe situated between the substrate and an associated polarizer layer.

Delamination of a coated layer such as a compensator or polarizer layeroften occurs in LCDs. To improve the interfacial adhesive forces betweenthe coated layer and the substrate, the layer-receiving surface of thesubstrate may be treated before coating by, for example, plasma orcorona discharge surface treatment, acid/base etching, or the like.These treatments are usually time-consuming and not always effective,particularly for certain substrates such as fluorinated compounds.

As an alternative to the foregoing surface treatments, adhesionpromoters such as acrylic polymers (an example of which is GeneralElectric's SHP401 primer) applied to the layer-receiving surface of thesubstrate have been used in an effort to prevent delamination. However,the interfacial forces provided by such adhesion promoters have oftenbeen inadequate to prevent delamination.

Another example of a laminated optical apparatus subject to delaminationis the window or dome structure that houses the optical sensors carriedby a missile. Such a dome structure may comprise a pair of adhesivelybonded optically transparent sapphire substrates or layers. The severeoperating environment of the missile subjects the dome structure to hightemperatures and mechanical stresses often causing separation of thedome layers along the adhesive bond.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, there is provided anadhesion promoter for enhancing the bond between adjacent layers of amultilayer structure to prevent delamination thereof. Examples ofmultilayer structures that may advantageously utilize the adhesionpromoter of the invention include, without limitation, liquid crystaldisplays and bonded missile domes.

Broadly, the adhesion promoter of the invention comprises an aromaticpolyimide-based UV-cured acrylate. More specifically but withoutlimitation, the adhesion promoter comprises an aromatic polyimide and aUV-cured resin, wherein the proportions by weight of the constituentsare effective to enhance the bond between adjacent layers of a laminatedstructure. Preferably, the relative proportions, by weight, of theconstituents are from 20% to 60% of the aromatic polyimide and from 40%to 80% of the UV-cured resin for a total of 100 parts of theconstituents.

Pursuant to another aspect of the invention there is provided a mixturefor producing an adhesion promoter, the mixture comprising (a) anaromatic polyimide; (b) a UV-curable resin; and (c) a solvent comprising(1) ethyl L-lactate and (2) isopropanol wherein the percentages byweight of the constituents (a), (b) and (c) are effective to produce anadhesion promoter for enhancing a bond between adjacent layers of alaminated structure. Preferably, the relative proportions, by weight, ofthe constituents (a), (b) and (c) are from 0.2% to 0.6% of (a), from0.4% to 0.8% of (b), from 55% to 64% of (c) (1) , and from 35% to 44% of(c) (2), for a total of 100 parts of (a), (b) and (c).

In accordance with a specific exemplary embodiment, there is provided aliquid crystal display comprising a pair of optically transparentsubstrates defining a liquid crystal cell, each substrate of the pair ofsubstrates having an outer surface carrying a multilayer structurecomprising in sequence from the outer surface an adhesive promoterlayer, a pressure sensitive adhesive layer, a second adhesion promoterlayer and an optical layer, each of the adhesive promoter layerscomprising an aromatic polyimide-based UV-cured acrylate.

In accordance with another specific exemplary embodiment, there isprovided a laminated structure comprising a first substrate and a secondsubstrate, the substrates being optically transparent at selectedwavelengths. A surface of the first substrate is in confrontingrelationship with a surface of the second substrate, and an adhesivelayer is disposed between the surfaces. A first UV-cured adhesionpromoter layer joins the surface of the first substrate and the adhesivelayer, and a second UV-cured adhesion promoter layer joins the surfaceof the second substrate and the adhesive layer. In one form of thisembodiment, the first and second layers are made of sapphire. In anotherform, each of the first and second adhesion promoter layers comprises anaromatic polyimide-based UV-cured acrylate. Preferably, each of theadhesion promoter layers comprises an aromatic polyimide and a UV-curedresin, wherein the percentages by weight of the constituents areeffective to enhance the bond between the surface of the associatedsubstrate and the adhesive layer.

Pursuant to another specific, exemplary embodiment of the invention,there is provided a method of fabricating a laminated, opticallytransparent structure comprising preparing a mixture by dissolving anaromatic polyimide and a UV-curable resin in a solvent, stirring themixture, filtering the mixture, coating the mixture on a surface of asubstrate, air drying the coated mixture, and curing the coated mixtureusing UV radiation, the cured coated mixture comprising an adhesionpromoter layer. The method may further comprise applying an opticallayer such as a compensator or polarizer over the cured adhesionpromoter coating.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages of the invention will becomeapparent from the detailed description, below, when read in conjunctionwith the accompanying drawings in which:

FIG. 1 is a schematic, cross section view of a portion of a laminatedoptical apparatus in the form of an LCD in accordance with a specific,exemplary embodiment of the present invention;

FIG. 2 is a schematic, cross section view of a portion of a laminatedoptical apparatus in the form of a missile dome in accordance withanother specific, exemplary embodiment of the present invention;

FIG. 3 is a flow chart showing an example of a process in accordancewith an aspect of the present invention for fabricating the apparatus ofFIG. 1; and

FIG. 4 is a flow chart showing an example of a process in accordancewith an aspect of the present invention for fabricating the apparatus ofFIG. 2.

DETAILED DESCRIPTION

The following description is of a best mode presently contemplated forpracticing the invention. This description is not to be taken in alimiting sense but is made merely for the purpose of describing thegeneral principles of the invention whose scope may be ascertained byreferring to the appended claims.

FIG. 1 is a schematic illustration of a portion of a laminated orlayered optical apparatus in the form of an LCD 10 incorporatingfeatures of the invention.

The LCD 10 comprises a liquid crystal cell 12 illuminated by a rearillumination source 14. The liquid crystal cell may comprise a twistednematic liquid crystal material 16 encapsulated between two opticallytransparent plates or substrates 18 and 20 of, for example, glass. Thesubstrates 18 and 20 carry typical LCD features (not shown) including,for example, color filters, thin film transistor multiplex driveelectronics, transparent electrodes and liquid crystal alignment filmson the source and viewer sides. Applied to an outer surface 22 of therear or source side liquid crystal cell substrate 18 is a multilayerstructure 23 comprising an adhesive promoter layer 24, a pressuresensitive adhesive (PSA) layer 26, a second adhesive promoter layer 28and, finally, a rear polarizer layer 30 adjacent to the rearillumination source 14. The PSA layer 26 may comprise any of a varietyof commercially available optically transparent PSA products from suchsuppliers as 3M, Sumitomo Chemical, Nitto Denko Corp., and so forth. Therear polarizer layer 30 may comprise, by way of example, a thin sheet ofstretched polyvinyl alcohol (PVA) stained with iodine.

In accordance with an aspect of the invention, the adhesion promoterlayers 24 and 28 are preferably fabricated of an aromaticpolyimide-based UV-cured acrylate. The adhesion promoter layers 24 and28 provide strong interfacial bonds between the PSA layer 26 and therear polarizer layer 30, and between the PSA layer 26 and the surface 22of the rear or source side liquid crystal cell substrate 18 preventingdelamination of the PSA and polarizer layers 26 and 30.

The PSA layer 26 may have a thickness in the range of, for example, 1 to2 μm. Each of the adhesion promoter layers 24 and 28 is very thin (forexample, less than 0.2 μm thick such as in the range of 0.05 to 0.15 μm)so as not to attenuate or otherwise affect light transmitted through theliquid crystal cell 12.

Overlying an outer surface 32 of the front or viewer side liquid crystalcell substrate 20 is a multilayer structure 34 like the structure 23 onthe source side of the cell 12. The multilayer structure 34 comprises anadhesive promoter layer 36, a PSA layer 38, a second adhesive promoterlayer 40, and a front polarizer layer 42 (commonly referred to as theanalyzer layer). The materials, thicknesses, and so forth of the frontside layers are preferably the same or substantially the same as thoseof the rear side layers.

Each of the adhesion promoter layers 24, 28, 36 and 40 may comprise, asconstituents, an aromatic polyimide and a UV-cured resin, thepercentages by weight of the constituents being effective to enhance thebond between adjacent layers of the LCD structure. By way of example,the relative proportions of the constituents may preferably comprise, byweight, from 20% to 60% of aromatic polyimide, and from 40% to 80% ofUW-cured resin for a total of 100 parts. More preferably, the relativeproportions of the constituents may comprise, by weight, from 30% to 50%of aromatic polyimide and from 50% to 70% of UV-curable resin for atotal of 100 parts. Most preferably, the relative proportions of theconstituents may comprise, by weight, from 35% to 45% and from 55% to65%, respectively, for a total of 100 parts.

FIG. 2 is a schematic illustration of a portion of another example of alaminated or layered optical apparatus utilizing features of the presentinvention. The apparatus of FIG. 2 is in the form of a high strength,bonded, optically transparent dome 50 forming part of a missile andincorporating features of the invention. The dome 50 may enclose one ormore of a variety of optical sensors for performing such tasks asmissile guidance and target acquisition. The dome 50 comprises an innersubstrate or layer 52 and an outer substrate or layer 54, each of thelayers 52 and 54 being formed of a high strength, heat resistantmaterial such as sapphire having the desired optical, mechanical andthermal properties.

The dome layers 52 and 54 are joined along confronting faces 56 and 58by means of an adhesive layer 60 comprising, for example, a UV cureclear silicone elastomer such as that supplied by Gelest, Inc., underthe trademark ZIPCONE™ UE. The adhesive layer 60 may be 1 to 2 μm thickand optically transparent to the wavelengths of interest, for example,3-5 μm. Interposed between the face 56 of the inner dome layer 52 andthe adhesive layer 60 is a UV-cured adhesion promoter layer 62. Asimilar UV-cured adhesion promoter layer 64 is interposed between theface 58 of the outer dome layer 54 and the adhesive layer 60. Inaccordance with an aspect of the invention, each of the adhesionpromoter layers 62 and 64 comprises an aromatic polyimide-based UV-curedacrylate providing high resistance to delamination of the dome layers 52and 54. Each of the adhesion promoter layers 62 and 64 is sufficientlythin, for example, less than 0.2 μm thick (such as in the range of 0.05to 0.15 μm) so as not to attenuate or otherwise affect the transmittedor received optical is preferably the same as that described above inconnection with FIG. 1.

The following are non-limiting examples of materials and fabricationprocesses that may be employed in practicing the invention.

The adhesion promoter of the invention preferably comprises a UV curablecomposition basically comprising a mixture of an aromatic polyimide,such as a segmented, rigid-rod aromatic polyimide, and a UV-curableacrylate photopolymer. In accordance with one, specific exemplaryembodiment, the adhesion promoter may be fabricated from the followingmaterials:

-   -   Aromatic polyimide: PYRALIN™ PI4700 (DuPont)    -   UV curable resin: Norland Optical Adhesive 68 (NOA 68) (Norland)    -   Solvent: Ethyl L-lactate (Spectrum) and Isopropanol (Aldrich)

EXAMPLE 1

FIG. 3 is a flow chart showing preferred steps for fabricating laminatedor layered structures utilizing aspects of the present invention. Forexample, an adhesion promoter mixture was prepared by dissolving (step70) 0.4 g of aromatic polyimide and 0.6 g of UV curable resin in asolvent comprising 59.4 g of ethyl L-lactate and 39.6 g of isopropanol,for a total of 100 g. The mixture was stirred (step 71) for about 2hours using a magnetic stirrer. The mixture was then filtered (step 72)through a filter membrane having a 0.45 μm pore size. The mixture wascoated (step 73) on a surface of a glass substrate by spin-coating at aspeed of 1,500 rpm for 30 seconds. Alternatively, the mixture may becoated on the surface of the substrate by, for example, dipping,spraying or brushing. The coating was air-dried (step 74) at atemperature of 50° C. for 10 minutes, and then UV-cured (step 75) in anitrogen atmosphere by means of a UV fusion lamp conveyor system withthe conveyor moving at a speed of 10 fpm, to form the final adhesionpromoter layer.

The relative proportions by weight of the adhesion promoter constituentsare preferably in the range of 0.2-0.6% of aromatic polyimide, 0.4-0.8%of UV curable resin, 55-64% of ethyl L-lactate and 35-44% isopropanolfor 100% of the mixture of the four constituents. More preferably, therelative proportions by weight may be 0.3-0.5% aromatic polyimide,0.5-0.7% UV curable resin, 57-62% ethyl L-lactate and 37-42% isopropanolfor 100% of the mixture, and most preferably the relative proportions byweight may be 0.35-0.45% aromatic polyimide, 0.55-0.65% UV curableresin, 59-60% ethyl L-lactate and 39-40% isopropanol for 100% of themixture.

In accordance with one exemplary application of the foregoing process,an optical layer (not shown) such as a polarizer or an opticalcompensator of, for example, a thin sheet of stretched PVA, may beapplied over the adhesion promoter layer prepared in steps 70-75 toprovide a strong, delamination-resistant bond between the substrate andthe overlying optical layer.

Alternatively, as further shown in FIG. 3, an LCD such as thatillustrated in FIG. 1 was fabricated by applying (step 76) a PSA layerto the adhesion promoter layer formed in steps 70-75, coating anacrylate mixture as prepared in steps 70-72 on a polarizer layer (step77), followed by air-drying and UV-curing of the coating (steps 78 and79) to form a second adhesion promoter layer in the manner described insteps 74 and 75, and applying the coated polarizer layer (step 80) tothe PSA layer.

Alternatively, for the percentage ranges of aromatic polyimide andisopropanol specified above, the solvent may comprise from 55% to 100%,by weight, of ethyl L-lactate and from 0% to 45%, by weight, ofisopropanol for 100 parts of the solvent.

EXAMPLE 2

FIG. 4 is a flow chart showing the steps of a preferred process forfabricating a laminated or layered optical structure such as that shownin FIG. 2. An adhesion promoter mixture of aromatic polymide, UV-durableresin and solvent was prepared by dissolving (step 82), stirring (step84) the mixture and filtering (step 86) as in Example 1. The mixture wascoated (step 88) on the surfaces of the first and second sapphiresubstrates as in Example 1. The coatings on the substrates wereair-dried (step 90) and UV-cured (step 92) as in Example 1 to form anadhesive promoter layer on each substrate. The substrates were thenbonded (step 94) by applying a layer of an optically transparentadhesive such as ZIPCONE™ UE mentioned above on the adhesion promoterlayer on one of the sapphire substrates and the two sapphire substrateswere then joined to form the structure depicted in FIG. 2. The relativeproportions by weight of the adhesion promoter constituents were thesame as those set forth in Example 1.

By way of example and not by way of limitation, the adhesion promoter ofthe present invention may be used to enhance adhesion between:

1. an organic substrate and an organic thin film;

2. an organic substrate and an inorganic thin film;

3. an organic substrate and an organic substrate;

4. an inorganic substrate and an inorganic thin film; and

5. an inorganic substrate and an inorganic substrate.

Examples of organic materials include, but are not limited to,polycarbonate, polypropylene, polyimide and fluorocarbon. Examples ofinorganic materials include, but are not limited to, oxide, fluoride andsulfide materials.

While several illustrative embodiments of the invention have beendisclosed herein, still further variations and alternative embodimentswill occur to those skilled in the art. Thus, the adhesive promoterforming one aspect of the invention is useful wherever the prevention offilm delamination is an important goal and accordingly is amenable to abroad range of applications including, besides those described above,the adhesive bonding between a window pane and a UV or IR protectivefilm, or between a polycarbonate headlight lens and an abrasionresistant hardcoat. Such variations and alternative embodiments arecontemplated, and can be made without departing from the spirit andscope of the invention as defined in the appended claims.

1. An adhesion promoter comprising an aromatic polyimide-based UV-curedacrylate.
 2. An adhesion promoter comprising as constituents: (a) anaromatic polyimide; and (b) a UV-cured resin, wherein the proportions byweight of the constituents (a) and (b) are effective to enhance the bondbetween adjacent layers of a laminated structure.
 3. The adhesionpromoter of claim 2 wherein: the relative proportions, by weight, ofsaid constituents (a) and (b) are from 20% to 60% of (a), and from 40%to 80% of (b) for a total of 100 parts of (a) and (b).
 4. The adhesionpromoter of claim 2 wherein: the relative proportions, by weight, ofsaid constituents (a) and (b) are from 30% to 50% of (a), and from 50%to 70% of (b) for a total of 100 parts of (a) and (b).
 5. The adhesionpromoter of claim 2 wherein: the relative proportions, by weight, ofsaid constituents (a) and (b) are from 35% to 45% of (a), and from 55%to 65% of (b) for a total of 100 parts of (a) and (b).
 6. A mixture forproducing an adhesion promoter, the mixture comprising as constituents:(a) an aromatic polyimide; (b) a UV-curable resin; and (c) a solventcomprising: (1) ethyl L-lactate; and (2) isopropanol, wherein thepercentages by weight of the constituents (a), (b) and (c) are effectiveto produce an adhesion promoter for enhancing a bond between adjacentlayers of a laminated structure.
 7. The mixture of claim 6 wherein: therelative proportions, by weight, of said constituents (a), (b) and (c)are from 0.2% to 0.6% of (a), from 0.4% to 0.8% of (b), from 55% to 64%of (c) (1), and from 35% to 44% of (c) (2), for a total of 100 parts of(a), (b) and (c).
 8. The mixture of claim 6 wherein: the relativeproportions, by weight, of said constituents (a), (b) and (c) are from0.3% to 0.5% of (a), from 0.5% to 0.7% of (b), from 57% to 62% of (c)(1), and from 37% to 42% of (c) (2), for a total of 100 parts of (a),(b) and (c).
 9. The mixture of claim 6 wherein: the relativeproportions, by weight, of said constituents (a), (b) and (c) are from0.35% to 0.45% of (a), from 0.55% to 0.65% of (b), from 59% to 60% of(c) (1), and from 39% to 40% of (c) (2) , for a total of 100 parts of(a), (b) and (c).
 10. A layered structure comprising: a first layerhaving a surface; a second layer having a surface confronting thesurface of the first layer; and an adhesion promoter layer joining theconfronting surfaces of the first and second layers, the adhesionpromoter comprising an aromatic polyimide-based UV-cured acrylate. 11.The structure of claim 10 wherein: the first layer comprises a materialselected from the group consisting of an inorganic material and anorganic material; and the second layer comprising a material selectedfrom the group consisting of an inorganic material and an organicmaterial.
 12. The structure of claim 10 wherein: the adhesion promoterlayer comprises as constituents: (a) an aromatic polyimide; and (b) aUV-cured resin, wherein the percentages by weight of the constituents(a) and (b) are effective to enhance the bond between adjacent layers ofa laminated structure.
 13. The structure of claim 12 wherein: therelative proportions, by weight, of said constituents (a) and (b) arefrom 20% to 60% of (a), and from 40% to 80% of (b) for a total of 100parts of (a) and (b).
 14. The structure of claim 13 wherein: therelative proportions, by weight, of said constituents (a) and (b) arefrom 30% to 50% of (a), and from 50% to 70% of (b) for a total of 100parts of (a) and (b).
 15. The structure of claim 13 wherein: therelative proportions, by weight, of said constituents (a) and (b) arefrom 35% to 45% of (a), and from 55% to 65% of (b) for a total of 100parts of (a) and (b).
 16. The structure of claim 10 wherein: Theadhesion promoter layer has a thickness in the range of 0.05 to 0.15 μm.17. A liquid crystal display comprising: a pair of optically transparentsubstrates defining a liquid crystal cell, each substrate of the pair ofsubstrates having an outer surface carrying an adhesion promoter layercomprising an aromatic polyimide-based UV-cured acrylate; and an opticallayer coated on the adhesion promoter layer.
 18. The display of claim 17wherein: the adhesion promoter comprises as constituents: (a) anaromatic polyimide; and (b) a UV-cured resin, wherein the percentages byweight of the constituents (a) and (b) are effective to enhance the bondbetween adjacent layers of a laminated structure.
 19. The display ofclaim 18 wherein: the relative proportions, by weight, of saidconstituents (a) and (b) are from 20% to 60% of (a), and from 40% to 80%of, (b) for a total of 100 parts of (a) and (b).
 20. The display ofclaim 18 wherein: the relative proportions, by weight, of saidconstituents (a) and (b) are from 30% to 50% of (a), and from 50% to 70%of (b) for a total of 100 parts of (a) and (b).
 21. The display of claim18 wherein: the relative proportions, by weight, of said constituents(a) and (b) are from 35% to 45% of (a), and from 55% to 65% of (b) for atotal of 100 parts of (a) and (b).
 22. The display of claim 17 wherein:the optical layer comprises a compensator.
 23. The display of claim 17wherein: the optical layer comprises a polarizer.
 24. The display ofclaim 17 wherein: The adhesion promoter coating has a thickness in therange of 0.05 to 0.15 μm.
 25. A liquid crystal display comprising: apair of optically transparent substrates defining a liquid crystal cell,each substrate of the pair of substrates having an outer surfacecarrying a multilayer structure comprising in sequence from said outersurface an adhesive promoter layer, a pressure sensitive adhesive layer,a second adhesion promoter layer and an optical layer, each of saidadhesive promoter layers comprising an aromatic polyimide-based UV-curedacrylate.
 26. The display of claim 25 wherein: each of said adhesivepromoter layers comprises as constituents: (a) an aromatic polyimide;and (b) a UV-cured resin, wherein the percentages by weight of theconstituents (a) and (b) are effective to enhance the bond betweenadjacent layers of a laminated structure.
 27. The display of claim 26wherein: the relative proportions, by weight, of said constituents (a)and (b) are from 20% to 60% of (a), and from 40% to 80% of (b) for atotal of 100 parts of (a) and (b).
 28. The display of claim 26 wherein:the relative proportions, by weight, of said constituents (a) and (b)are from 30% to 50% of (a), and from 50% to 70% of (b) for a total of100 parts of (a) and (b).
 29. The display of claim 26 wherein: therelative proportions, by weight, of said constituents (a) and (b) arefrom 35% to 45% of (a), and from 55% to 65% of (b) for a total of 100parts of (a) and (b).
 30. The display of claim 25 wherein: the opticallayer comprises a compensator.
 31. The display of claim 25 wherein: theoptical layer comprises a polarizer.
 32. The display of claim 25wherein: each of said adhesion promoter layers has a thickness in therange of 0.05 to 0.15 μm.
 33. A laminated structure comprising: a firstlayer optically transparent at selected wavelengths; a second layeroptically transparent at said selected wavelengths, a surface of saidfirst layer being in confronting relationship with a surface of saidsecond layer; an adhesive layer between said surfaces; a first UV-curedadhesion promoter layer interposed between and joining the surface ofthe first layer and the adhesive layer; and a second UV-cured adhesionpromoter layer interposed between and joining the surface of the secondlayer and the adhesive layer.
 34. The structure of claim 33 wherein:said first and second layers are made of sapphire.
 35. The structure ofclaim 33 wherein: each of the first and second adhesion promoter layerscomprises an aromatic polyimide-based UV-cured acrylate.
 36. Thestructure of claim 33 wherein: each of the adhesion promoter layerscomprises as constituents: (a) an aromatic polyimide; and (b) a UV-curedresin, wherein the percentages by weight of the constituents (a) and (b)are effective to enhance the bond between adjacent layers of a laminatedstructure.
 37. The structure of claim 36 wherein: the relativeproportions, by weight, of said constituents (a) and (b) are from 20% to60% of (a), and from 40% to 80% of (b) for a total of 100 parts of (a)and (b).
 38. The structure of claim 36 wherein: the relativeproportions, by weight, of said constituents (a) and (b) are from 30% to50% of (a), and from 50% to 70% of (b) for a total of 100 parts of (a)and (b).
 39. The structure of claim 36 wherein: the relativeproportions, by weight, of said constituents (a) and (b) are from 35% to45% of (a), and from 55% to 75% of (b) for a total of 100 parts of (a)and (b).
 40. The structure of claim 33 wherein: each of the adhesionpromoter layers has a thickness in the range of 0.05 to 0.15 μm.
 41. Amethod of fabricating a laminated, optically transparent structurecomprising: preparing a mixture by dissolving an aromatic polyimide anda UV-curable resin in a solvent; stirring the mixture; filtering themixture; coating the mixture on a surface of a substrate; air drying thecoated mixture; and curing the coated mixture using UV radiation, thecured coated mixture comprising an adhesion promoter layer.
 42. Themethod of claim 41 further comprising: applying an optical layer overthe cured adhesion promoter coating.
 43. The method of claim 42 wherein:the optical layer comprises an optical element selected from the groupconsisting of a compensator and a polarizer.
 44. The method of claim 41wherein: the relative proportions, by weight, of said aromaticpolyimide, UV-curable resin and solvent are, respectively, in the rangesof 0.35% to 0.45%; 0.55% to 0.65%; and 98.9% to 99.1%, by weight. 45.The method of claim 41 wherein: the solvent comprises as constituentsethyl L-lactate and isoproponal.
 46. The method of claim 45 wherein: therelative proportions, by weight, of the solvent constituents comprise55% to 100% of ethyl L-lactate and 0% to 45% of isoproponal, for a totalof 100 parts of the solvent.
 47. The method of claim 41 wherein: thecoated mixture has a thickness in the range of 0.05 to 0.15 μm.
 48. Themethod of claim 41 further comprising: coating the mixture on a surfaceof a second substrate; air drying the coated mixture on the surface ofthe second substrate; curing the coated mixture on the surface of thesecond substrate using UV radiation, the cured coated mixture on thesecond substrate comprising an adhesion promoter layer; and bonding thefirst and second substrates together using an adhesive between theadhesion promoter layers on the first and second substrates.
 49. Themethod of claim 48 wherein: the first and second substrates comprisesapphire.
 50. A method of using an aromatic polyimide-based UV-curableacrylate, the method comprising: depositing a coating of said aromaticpolyimide-based UV-curable acrylate on the surface of a first layer;curing said coating using UV radiation; and applying a second layer onthe UV-cured coating, said coating preventing separation of said layers.51. The method of claim 50 wherein: the first layer comprises a materialselected from the group consisting of an inorganic material and anorganic material; and the second layer comprises a material selectedfrom the group consisting of an inorganic material and an organicmaterial.
 52. The method of claim 50 wherein: the coating of saidaromatic polyimide-based UV-curable acrylate has a thickness in therange of 0.05 to 0.15 μm.
 53. A mixture for producing an adhesionpromoter, the mixture comprising: (a) an aromatic polyimide; (b) aUV-curable resin; and (c) a solvent, wherein: (a) is present in anamount from 0.2% to 0.6% of the mixture by weight; (b) is present in anamount from 0.4% to 0.8% of the mixture by weight, and wherein (c)comprises the remainder of the mixture and comprises from 55% to 100%,by weight, of ethyl L-lactate and from 0% to 45%, by weight, ofisopropanol.